We aim to assess whether respiratory symptoms are associated with lung function in young adults, and whether any such relation is similar in those with asthma, in men and women, and in different countries. Study participants (aged 20-44 years) were randomly selected from the general population in 35 centres in 15 countries as part of the European Community Respiratory Health Study. In all, 12,541 subjects (47%) completed a respiratory symptoms questionnaire and spirometry, metacholine challenge and immunoglobulin E tests. Indicators of diagnosed asthma showed the largest association with airways obstruction (FEV1--maximal 1-s forced expiratory volume/forced vital capacity--FVC < 70%), followed by symptoms of wheezing or shortness of breath, in both genders. Among the 96% of subjects whose FEV1/FVC ratios were greater or equal to 70%, wheezing or shortness of breath was associated with lower FEV1 levels (-211 ml in men and -169 ml in women (P < 0.01)), independent of diagnosed asthma, smoking, atopy or bronchial responsiveness. This association was not explained by a lower FVC. Symptoms of chronic bronchial mucus hypersecretion (chronic phlegm) were unrelated to both airways obstruction and FEV1 levels. Findings were homogeneous across all centres. These results suggest that lung diseases that cause wheezing are generally associated with impaired lung function.